Process for making flameproofed, water-resistant paper



United States Patent Oflice 2,986,478 Patented May 30, 1961 PROCESS FOR MAKING FLAMEPROOFED, WATER-RESISTANT PAPER Charles R. Outterson, Richmond, Va., assignor to The Alhemarle Paper Manufacturing Company, Richmond, Va., a Corporation of Virginia No Drawing. Filed Oct. 29, 1958, Ser. No. 770,278

12 Claims. (Cl. 117-137) This invention relates to a process for making flameproof, water-resistant paper.

As pointed out in my copending application S.N. 569,689, filed March 6, 1956, for Process for Flameproofing Paper, issued January 6, 1959, U.S. 2,867,549, the paper making art had not been able successfully to produce a rosin sized paper, flameproofed with water soluble flameproofing salts, which was water resistant, leach proof and could meet flameproofing standards. To a very substantial extent, these difficulties were overcome by the process disclosed in said copending application, which comprises impregnating an at least partially sized paper with a rosin suspension containing water-soluble flameproofing salts having a maximum pH of about 7, and then drying the paper. The paper made in this fashion meets flameproof standards, has substantial water resistance as measured in accordance with ASTM Designation D779-54, e.g. up to about 40 to 60 seconds, and retains its flameproofness under conditions of high humidity and superficial moistening.

The object of this invention is to provide a process for making a rosin-sized paper containing petroleum wax as an additional sizing component and flameproofed with water-soluble salts, which is an improvement over the process of my said copending application in terms of simplicity and economy of operation, and which produces an improved product.

A primary object is to produce a paper product of greatly increased water resistance.

Another object is to provide a process which reduces the amount of flameproofing salts required, thereby increasing the strength of the paper by increasing the ratio of paper fiber to salts for a given paper weight.

Still another object is the elimination of the necessity for preliminary sizing of the paper furnish with such corollary advantages as providing complete freedom in the reworking of acid broke in the beater.

Another object is to broaden the area of waterproofing salts available for use in the process to include flameproofing salts and mixtures of flameproofing salts which are alkaline as well as those which are neutral or acid.

Still another object is to provide a sizing and flameproofing process which minimizes corrosion of the equipment and improves operating difliculties by reducing breakage on the paper machine.

Broadly speaking my invention comprises impregnating unsized or sized paper, preferably unsized, with an aqueous solutionof water-soluble flameproofing salts containing finely divided particles of a rosin-petroleum wax mixture in stable emulsion, and then heat drying the paper in the usual fashion.

I have found that when a suspension of particles comprising an intimately blended mixture of rosin and petroleum wax in an aqueous solution of water soluble flameproofing salts is applied to a highly absorbent, namely unsized, paper, the paper is flameproofed to a degree far exceeding minimum standard requirements and is rendared so highly water-resistant that it can even withstand actual soaking in water without leaching of the watersoluble flameproofing salts in sufiicient quantity to destroy its flame resistance. These remarkable results, furthermore, are obtained with a reduced amount of flameproofing salts.

A similar treatment employing wax alone as the solid disperse phase confers a substantial degree of water resistance to the paper and flameproofing salts. However, when the paper is dried after impregnation as, for example, on the conventional drum driers, the wax migrates to the surface of the paper opposite that in contact with the heating unit, forming a thin surface film of highly combustible wax. When a torch is applied, a sheet of flame is propagated almost instantaneously over the entire surface of the paper. Although the paper itself may not ignite, such a sheet of flame would obviously be exceedingly hazardous in many areas of use.

As disclosed in my earlier copending application, an aqueous solution of flameproofing salts containing rosin alone as the solid disperse phase, does not confer the requisite flameproofness when app-lied to an unsized paper. The highly absorbent fibers apparently rapidly absorb the aqueous phase containing the flameproofing salts, removing it from the particles of rosin which deposit outside of and between the fibers, and leaving the rosin unprotected and combustible.

There is a marked difference in the behavior of molten wax and molten rosin on paper. The former migrates rapidly throughout the body of the paper whereas the latter remains localized. This is clearly demonstrated by a test such as the following.

One gram pieces of paraflin wax having a melting point of about 122 F. and rosin having a melting point of about F. were each placed on 6" by 6" sheets of paper, which had previously been impregnated with flameproofing salts an ddried. The sheets were then placed in an oven at a temperature above the melting points of the wax and rosin, namely at 212 F., and allowed to remain until the wax and rosin had melted as shown by their leveling out on the paper. Upon withdrawal of the samples from the oven, it was found that the rosin had spread over less than 1 square inch of the paper whereas the wax had spread throughout the entire 36 square inches of the sheet.

As a result of these markedly different aflinities of petroleum wax and rosin, under the heat of the paper driers, which in conventional practice is generally about 250 to 350 F., wax particles melt and the melted wax quickly migrates throughout the paper with concomitant coating of the fibers. Rosin particles, on the other hand, thorugh molten, remain substantially localized with relatively little coating of the fibers.

By blending suitable proportions of petroleum wax and rosin into an intimate mixture and thereby producing a plastic composition which has an aflinity for the cellulosic fibers intermediate that of the individual wax and rosin components, I have found that the excessive migration of the wax can be controlled and reduced so that it does not form a combustible layer on the surface of the paper. Although I do not wish to be confined by any theoretical explanations, I believe that the markedly improved results produced by the instant invention is due to melting of the discrete particles of the wax-rosin mixture, deposited on and between the fibers from the aqueous flameproofing suspension, by the heat of the driers, and suflicient controlled migration of the molten mixture to flow about and coat the adjacent surrounding fibers which have absorbed the aqueous phase of the suspension and are, therefore, uniformly impregnated with the flameproofing salts. This thin, water-insoluble, protective coating on the fibers prevents leaching of the water-soluble salts and imparts a very high degree of water resist;

ance to the paper. Water resistance of paper treated in this manner, as measured according to ASTM D779-54, is at least 2 minutes, generally higher than 5 minutes and, in some cases 40 minutes or more. Papers dried, after these wetting periods, were found by tests to retain sufficient flameproofness to meet the standards set by T5-5282, Commercial Standard for Flame-Resistant Paper and Paperboard, which sets a maximum char length of 5.5 inches and a maximum afterglow of 2 seconds.

Since the'water resistant coating is in such intimate contact with the fibers relatively little fiameproofing salt is required exteriorly of the fibers to protect the combustible wax-rosin size. This makes possible a reduction of the amount of flameproofing salts required and eliminates the necessity for pre-sizing to reduce absorbency of the fibers. Where rosin alone is used as the sizing component in the suspension, the rosin particles, even after subjection to the elevated drying temperatures, tend to remain as relatively large, discrete entities outside the fibers requiring substantial amounts of the flameproofing salts for protection. To achieve this, absorbency of the fibers must be reduced by pre-sizing to ensure sufficien-t of the aqueous phase containing the salts to remain outside the fibers to protect the rosin. Since such fibers are not uniformly impregnated throughout with the protective salts, larger concentrations of the salts are required both in the impregnated portion of the fibers and without.

Where an aqueous rosin suspension of fiameproofing salts is applied to a pre-sized paper, the add-on of salts must be at least about lbs. and preferably about 17 lbs. per 100 lbs.- of paper, for adequate flameproofing. The add-on of salts required for adequate fiameproofness where an aqueous rosin-wax blend suspension of flameproofing salts is applied to an unsized paper is generally about 10 to 11 lbs. per 100 lbs. of paper.

The reduction in the amount of required flameproofing salts not only is an economy factor but has several other important advantages. It makes possible an increase in the ratio of paper fiber to salts for a given weight of paper, thereby providing a stronger paper and, in the case of thin, light weight papers, improving processing by reducing breaks on the paper making machine because of the greater strength of the paper web. The reduced add-on requirement combined with the high absorbency of the non-pre-sized paper fibers makes possible more rapid impregnation of the paper at lower temperatures of the treating solution, thereby reducing the corrosive efiect of the fiameproofing salts on the equipment. Elimination of the pre-siziug requirement also removes processing problems posed by the reworking of acid flameproofed broke in the beater together with rosin size.

My new flameproofing treatment can also be applied to pre-sized paper. This may be desirable in certain grades of paper where some preliminary sizing improves machine operations. The reduced absorbency of the paper fibers necessitates an increase in the amount of flameproofing salts required. However, the same improvement in Water resistance of the paper and impregnating fiameproofing salts is obtained as in the case of the treatment of unsized paper.

To be suitable for my purpose, the petroleum wax and rosin must be intimately mixed or blended prior to dispersion. This can be accomplished by melting the wax and rosin and mixingthem thoroughly in the molten state. Substantially any type of petroleum wax can be used, including paraffin, petrolatum, scale, and microcrystalline wax. To achieve the desired migration control, the rosin or wax should preferably constitute at least about 20% by weight of the plastic blend. In other words, 'the ratio of rosin to wax can vary from about 20:80 to 80:20. The preferred ratio is 40:60 to :20.

Because of the high concentrations of the fiarneproofing salts in the aqueous phase, therosin-wax blend suspension should be stable toelectrolytes. Such electrolyte stable dispersions can be prepared in any desired manner as, for example, with the aid of a protective colloid such as gum arabic, gum acacia, casein, animal glue, starch and the like, which stabilizes the dispersed rosin-wax particles against agglomeration. It may also sometimes be desirable to include a surface active dispersing or emulsifying agent such as the alkyl or aralkyl sulfates and sulfonates, sulfonated vegetable oils, lignosulfonate and the like. A typical method of preparing an electrolytestable rosin-wax suspension is illustrated in the following example.

Example I 5 lbs. of a dispersing agent, such as sodium lignosulfonate, and 15 lbs. of a protective colloid, such as gum arabic, are dissolved in 500 lbs. water and the solution heated to 180 F. 500 lbs. melted plastic consisting of an intimate blend of 400 lbs. gum rosin and lbs. scale wax (M.P. 124-l26 F.) are slowly pumped into the hot solution with vigorous stirring for about 15 to 20 minutes. plastic preferably to about an average of 1 to 2 microns, the emulsion is passed through a colloid mill or other high speed dispersion apparatus.

Suitable.electrolyte-stable dispersions of difiering prop erties can be prepared in this manner by varying the proportion of rosin to wax and by using waxes of different properties. This makes possible closely controllable adjustment of the migrating tendency of the sizing blend and provides for such difiering conditions as the drying temperature and drying time required for different weights of paper at various paper machine speeds.

Example 11 An electrolyte-stable dispersion was prepared as in Example I, except that 500 lbs. of a melted plastic blend consisting of 250 lbs. gum rosin and 250 lbs. paraflin wax (M.P. 128-130 F.) was substituted for the rosin-wax blend used therein.

Example III An electrolyte-stable dispersion was prepared as in Example I, except that 500 lbs. of a melted plastic blend consisting of 250 lbs. gum rosin and 250 lbs. microcrystalline wax (Socony Mobil Oil Co. No. 2300, M.P. 155 F.) replaced the rosin-wax blend used therein.

Example IV The process of Example I was repeated except for substitution of 500 lbs. of a melted plastic blend of 100 lbs. black wax (M.P. F.) and 400 lbs. wood rosin for the rosin-wax blend used therein.

Example V The process of Example I was repeated except for substitution of 500 lbs. of a melted plastic blend consisting of 250 lbs. crude petrolatum wax (M.P. 130-135 F.) and 250 lbs. wood rosin for the rosin-wax blend used therein.

The amount of rosin-wax blend applied to the paper in the combined sizing and flameproofing treatment is determined largely by the amount of flameproofing salts introduced. weight of the salts is entirely adequate, although in some cases it may be as low as 1.0% or as high as 4 to 5%. The proportion of the rosin-wax blend can be increased as much as desired as, for example, up to 10%or more,

althoughpractical limitations will be imposed by consideration of cost and the physical characteristics of the finished paper.

Any suitable water-soluble flameproofing salt or mixture of salts can be used for my purpose. The pH of the salts can be acid, neutral or alkaline. Alkaline salts cannot successfully be employed where rosin alone is employed as the sizing agent since such alkaline salts in the finished paper tend to'saponify the rosin, thereby solubilizing it and destroying its water resistant protective To reduce the particle size of the emulsified In general about 2 to 3% based on the action. I have found, however, that the protective and sizing action of the rosin-wax blends is not adversely affected by alkaline salts such as diammonium orthophosphate. The reason for this remarkable phenomenon is not clearly understood but the wax in the intimate waxrosin blend or solution apparently protects the rosin against saponification by the alkaline salts.

Examples of flameproofing salts which are particularly suitable because of their eflicacy, low cost and availability include ammonium sulfate, monoammonium orthophosphate, ammonium chloride, and diammonium-orthophosphate. Other well-known water-soluble flameproofing salts can be employed as well, although, in general, it is preferable to minimize the use of salts having metallic cations which might promote afterglow.

The flameproofing salts are dissolved in the aqueous phase of the rosin-wax particle suspension and incorporated into the paper in an amount sutficient to provide the desired flameproofness. The actual amount incorporated into the treating suspension is, of course, determined by conditions such as the total fluid pick-up by the paper under the particular conditions of application, which in turn determines the requisite solids concentration in the suspension. For example, where the fluid pick-up is 50% by weight of the paper, solids concentration in the suspension should be twice the desired solids add-on on a dry paper basis.

In general a flameproofing salt add-on of about 10 to 11% is adequate where the suspension is applied to a highly absorbent unsized paper, though more can be in corporated if desired. Where absorption of the fibers is reduced by pre-sizing, the salt add-on required is generally higher, e.g. up to about 15 to 17%.

The paper can be impregnated with the rosin-wax particle suspension containing the flameproofing salts in solution in any desired and convenient manner, as by dipping, spraying, rotating brushes, contact rolls and the like.

Example VI 100% unbleached kraft pulp (pine) with no size or alum was refined to Canadian freeness 542 to 556 and run into base paper having a basis weight of 89.5 pounds per ream of 500 sheets size 24 X 36 inches. The paper tested -1 second water resistance according to ASTM D779-54.

A. The dry unsized paper was passed through a size press on the paper machine at a speed of 340 ft./min. and impregnated with a two phase system prepared as follows:

(NH SO 4600 lbs. (NH HPO 100 lbs. Rosin-wax suspension (prepared as in Example HI) 22 gal. (2.2% rosin-wax blend on salts).

This formula was made up in a 1500 gallon tank and adjusted with water to 28% solids. The two phase system was applied to the paper at 134 F. The pick-up increased the dry weight of the paper from 89.5 to 101 lbs. per ream (11.4%

The paper was tested in accordance with ASTM D777- 46 with the following results:

Char length:

In machine direction 2.5 inches.

In cross direction 2.6 inches. Afterglow Less than 1 second.

These results conform with T5-5282, Commercial Standard for Flame-resistant Paper and Paperboard, recommended by the US. Department of Commerce.

All samples tested showed no penetration after 5+ minutes. Since 5+ minutes indicates outstanding water resistance, further timing was discontinued.

The 5+ minute test papers were dried and retested for flameproofing. All conformed with T5-5282 standards, although the char test advanced from 2.5 to 4.5 inches.

B. The same base paper was impregnated with a 28% 6 solution of the same flameproofing salts as in A without the rosin-wax suspension. The paper picked up about 11% of the flameproofing salts. Char length was the same and afterglow about 1 second. Water resistance was 1 second. After drying of the wetted sample, it failed to meet flameproofing specifications.

C. The same base paper was impregnated with a flameproofing composition similar to that in A except that a rosin suspension, 2.2% solids on dry salts, was substituted for the rosin-wax blend suspension. Char length was similar but afterglow extended beyond the permitted 2 seconds, so that the paper failed to meet the commercial standard.

D. The same base paper was impregnated as in A except that a wax suspension, 2.2% solids on the dry salts, was substituted for the rosin-wax blend. Char. length and afterglow were satisfactory but upon application of the torch, a sheet of blue flame travelled almost instantaneously over the entire surface of the sample.

Example VII Example VIII unbleached kraft pulp (pine) was refined to Canadian freeness 600, no size or alum added (pH 8.0), and run into paper having a basis weight of pounds per ream of 500 sheets (24 x 36"). At the size press, the dry sheet was passed through an aqueous bath containing 30% diammonium phosphate and 2% on the salt of a dispersed rosin-wax blend prepared as in Example III. The pick-up was 14.7% diammonium phosphate.

Tests for flame resistance:

Char length:

Machine direction 1.5 inches.

Cross direction 1.5 inches. Afterglow Less than 1 second.

The flameproofed paper was tested for water resistance and showed no penetration after 2 minutes. The Wet samples were dried out and again tested for flame resistance:

Char length:

Machine direction inches 2.5 Cross direction do 3 Afterglow seconds 1 Example IX 100% unbleached kraft pulp (pine) was sized lightly with rosin size in the beaters and run into base paper having a basis weight of 25 pounds per ream (500- 24 x 36"). The paper tested five seconds water resistance according to ASTM D779-54.

A. The dry, lightly sized sheet was passed through a size press on the paper machine at a speed of 800 feet/ minute and impregnated at a temperature of F. with an aqueous two phase system containing 35% (NH SO and 2.1% electrolyte stable rosin emulsion (rosin solids on dry salt). The pick-up of flameproofing salts was approximately 17+%.

Tests for flame resistance:

Afterglow seconds 1 .7 i The finished flamep roofed'pape'r was tested for water resistance, All samples resisted 40 seconds;j"a few were .-tested'further,'and were penetrated by the water in one :minute. The wet-test samples were dried and again .tested for flame resistance. Char lengthsran tjov 4.5 inches. B. The same base paper as in A was passed through a size press on the paper machine at a speed ofx800'feet/ minute and impregnated at a temperature of140 -F. with-arr aqueous two phase system containing 36.2% (NH4) SO and 2.2% electrolyte stable rosin-wax blend emulsion- (solids on'dry salt) prepared according to Example IV. Thepick-up of flameproofin'g salt in the sheet Tests for flame resistance:

.Char length; 7

j Machine direction 'inches 3.2 p Cross direction 'do 3.4 Afterglow seconds 1 The finished flameproofed paper was tested for water resistance. All samples resisted penetration for 2+ minutes. at which time further testing was discontinued. The wet samples were dried and again tested for flame resistance, Char lengths and aftergow remained substantially unimpaired.

Although this invention has been described with reference to illustrative embodiments thereof, it will be apparent to those skilled in the art that it may be embodied in. other. forms but within the scope of the appended claims.

Iclaim: V a

l. A process for fiameproofing paper which comprises impregnating a paper sheet with an aqueous suspension of blended rosin and petroleum wax in the form of particles, each of said particles consisting essentially of said rosin and petroleum wax in intimately blended admixture in a solution of water-soluble fiameproofing salts, the flameproofing salts being incorporated in the paper in an amount suflicient to render said paper substantially flameproof, said rosin-petroleum wax blend being incorporated in the paper in an amount sufficient to impart substantial water resistance to said water-soluble salts, and then drying the paper.

2. The process of claim 1 in which the ratio of rosin to petroleum wax in'the blend ranges from about 80:20 to 20:80. 7

3. The process of' clairn [in which the ratio of rosin to petroleum 'wax intheblend ranges from about 40:60

4'. The process of claim lin which the fiameproofing salts are selected from the group consisting of ammonium sulfate; 'arnr'noniumchloride, monoarnmonium phosphate, diammonium phosphate, and mixtures thereof.

5. The process of claim 2 in which the flameproo'fing salts are selected from the group consisting of-ammonium sulfate, ammonium chloride, mono-ammonium phosphate, diammonium phosphate, and mixtures thereof.

6. A process for flamcproofing paper which comprises impregnating an'unsized paper sheet with aqueous suspension of blended rosin and petroleum wax in the form of particles, each of said particles'consisting essentially of said rosin and petroleum ,wax in intimately blended admixture in a solution of water-soluble flameproofing salts, the flarneproofing salts being incorporated in the paper in an amount sufiicient to render said paper substantially fiameproof, said rosin-petroleum wax blend being incorporated in the paper in an amount sufficient to impart substantial water resistance to said watersoluble salts, and then drying the paper.

7. The process of claim 6 in which the ratio of rosin to petroleum wax in the blend ranges from about 80:20 to 20:80.

8. The process of claim 6 in which the ratio of rosin to petroleum wax in the blend ranges from about 40:60 to 80:20.

9. The process of claim 6 in which the fiameproofing salts are selected from the group consisting of ammonium sulfate, ammonium chloride, phosphate, diammonium phosphate, and mixtures thereof.

10. The process of claim 7 in which the fiameproofing salts are selected from the group consisting of ammonium sulfate, ammonium chloride, monoammonium phosphate, diammonium phosphate, and mixtures thereof. 11. The process of claim 6 in which the flameproofing salt comprises at least about 10% by weight of the paper.

12. The process of claim 7 in which the fiameproofing salt comprises at least about 10% by weight of the paper.

References Cited in the file of this patent UNITED STATES PATENTS 2,637,665 Dodge May 5, 1953 2,838,806 Sabine June 17, 1958 2,867,549 Outterson Jan. 6, 1959 2,868,665 McManus Jan. 13, 1959 monoammonium 

1. A PROCESS FOR FLAMEPROOFING PAPER WHICH COMPRISES IMPREGNATING A PAPER SHEET WITH AN AQUEOUS SUSPENSION OF BLENDED ROSIN AND PETROLEUM WAX IN THE FORM OF PATTICLES, EACH OF SAID PARTICLES CONSISTING ESSENTIALLY OIF SAID ROSIN AND PETROLEUM WAX IN INTIMATELY BLENDED ADMIXTURE IN A SOLUTION OF WATER-SOLUBLE FLAMEPROOFING SALTS, THE FLAMEPROOFING SALTS BEING INCORPORATED IN THE PAPER IN AN AMOUNT SUFFICIENT TO RENDER SAID PAPER SUBSTANTIALLY FLAMEPROOF, SAID ROSIN-PETROLEUM WAX BLEND BEING INCORPORATED IN THE PAPER IN AN AMOUNT SUFFICIENT TO IMPART SUBSTANTIAL ATER RESISTANCE TO SAID WATER-SOLUBLE SALTS, AND THEN DRYING THE PAPER. 